"Let's find out," Sirius says, and dives under the surface. As he passes beneath Shimmer, he runs his tail-tip along the length of her underside, and reflects that in some respects, water makes a better element for tickle matches because neither dragon can press parts of their bodies to the ground to keep them out of reach.

He sees that much of the lake is shallow, but that toward the center it is as deep as the nose-to-tail length of four or five dragons. Also, deeper down, it becomes dark enough that two dragons swimming down there would not be able to see one another unless they were almost nose to nose.

Sirius swims down, heading for the deep part of the lake. He darts down into the dark waters, waiting till he gets deep enough that visibility is difficult. When he decides he's reached that point, he suddenly changes direction, wondering if Shimmer will see him and follow him in the turn, or keep going past him. He cannot see her, but listens for the sound of her moving through the water.

Sirius disappears into the darkness and shimmer looses sight of him. "Where'd he go?" She slows down a little but keeps swimming in the same direction. She extends her hind paws down into the darkness and spreads her toes slightly, expecting to find the muddy bottom to protect her most vulnerable point.

Sirius chuckles as Shimmer retreats back into the darkness. He listens for her, but now can't hear her. Moving slowly, with his head turning from side to side, he lets himself sink lower into the dark water, trying to detect her either by sight or hearing. But in this darkness, the two dragons would have to be nearly touching to actually see one another.

Sirius wriggles like an eel, trying to get out of Shimmer's grasp. He realizes that when underwater, one tends to run out of air more quickly when being tickled, so he knows he's got to get to the surface soon.